Control channel design for machine type communications

ABSTRACT

Aspects of the present disclosure provide techniques that may be applied in systems to allow for communication over a control channel utilizing a relatively narrow band (e.g., six physical resource blocks) based search space. An exemplary method, performed by a user equipment, generally includes identifying, within a subframe, a first search space to monitor for a downlink control channel that occupies a first number of physical resource blocks (PRBs) that represents a narrowband size and monitoring at least the first search space for the downlink control channel transmitted in the subframe.

CLAIM OF PRIORITY UNDER 35 U.S.C. § 120

This application is a continuation of U.S. patent application Ser. No.14/886,898, filed Oct. 19, 2015, which claims benefit of and priority toU.S. Provisional Patent Application Ser. No. 62/066,305, filed Oct. 20,2014, both of which are hereby assigned to the assignee hereof andhereby expressly incorporated by reference herein in their entireties asif fully set forth below and for all applicable purposes.

BACKGROUND I. Field

Certain aspects of the present disclosure generally relate to wirelesscommunications and, more particularly, to control channel designs forcertain wireless devices, such as machine type communication(s) (MTC)devices.

II. Background

Wireless communication systems are widely deployed to provide varioustypes of communication content such as voice, data, and so on. Thesesystems may be multiple-access systems capable of supportingcommunication with multiple users by sharing the available systemresources (e.g., bandwidth and transmit power). Examples of suchmultiple-access systems include code division multiple access (CDMA)systems, time division multiple access (TDMA) systems, frequencydivision multiple access (FDMA) systems, 3rd Generation PartnershipProject (3GPP) Long Term Evolution (LTE)/LTE-Advanced systems andorthogonal frequency division multiple access (OFDMA) systems.

Generally, a wireless multiple-access communication system cansimultaneously support communication for multiple wireless terminals.Each terminal communicates with one or more base stations viatransmissions on the forward and reverse links. The forward link (ordownlink) refers to the communication link from the base stations to theterminals, and the reverse link (or uplink) refers to the communicationlink from the terminals to the base stations. This communication linkmay be established via a single-input single-output, multiple-inputsingle-output or a multiple-input multiple-output (MIMO) system.

To enhance coverage of certain devices, such as MTC devices, “bundling”may be utilized in which certain transmissions are sent as a bundle oftransmissions, for example, with the same information transmitted overmultiple subframes.

SUMMARY

Certain aspects of the present disclosure provide techniques andapparatus for communicating control channels to certain devices, such asmachine type communication (MTC) UEs.

Certain aspects of the present disclosure provide a method for wirelesscommunications by a user equipment (UE). The method generally includesidentifying, within a subframe, a first search space to monitor for adownlink control channel that occupies a first number of physicalresource blocks (PRBs) that represents a narrowband size and monitoringat least the first search space for the downlink control channeltransmitted in the subframe.

Certain aspects of the present disclosure provide an apparatus forwireless communications by a user equipment (UE). The apparatusgenerally includes means for identifying, within a subframe, a firstsearch space to monitor for a downlink control channel that occupies afirst number of physical resource blocks (PRBs) that represents anarrowband size and means for monitoring at least the first search spacefor the downlink control channel transmitted in the subframe.

Certain aspects of the present disclosure provide an apparatus forwireless communications by a user equipment (UE). The apparatusgenerally includes at least one processor configured to identify, withina subframe, a first search space to monitor for a downlink controlchannel that occupies a first number of physical resource blocks (PRBs)that represents a narrowband size and monitor at least the first searchspace for the downlink control channel transmitted in the subframe.Additionally, the apparatus generally includes a memory coupled with theat least one processor.

Certain aspects of the present disclosure provide a computer programproduct for wireless communications by a user equipment (UE) comprisinga computer readable medium having instructions stored thereon. Theinstructions, when executed by at least one processor, causes theprocessor to identify, within a subframe, a first search space tomonitor for a downlink control channel that occupies a first number ofphysical resource blocks (PRBs) that represents a narrowband size andmonitor at least the first search space for the downlink control channeltransmitted in the subframe.

Certain aspects of the present disclosure provide a method for wirelesscommunications by a base station (BS). The method generally includesidentifying, within a subframe, a first search space for a userequipment (UE) to monitor for a downlink control channel that occupies afirst number of physical resource blocks (PRBs) that represents anarrowband size and transmitting one or more downlink control channelsto the UE in the first search space.

Certain aspects of the present disclosure provide an apparatus forwireless communications by a base station (BS). The apparatus generallyincludes means for identifying, within a subframe, a first search spacefor a user equipment (UE) to monitor for a downlink control channel thatoccupies a first number of physical resource blocks (PRBs) thatrepresents a narrowband size and means for transmitting one or moredownlink control channels to the UE in the first search space.

Certain aspects of the present disclosure provide an apparatus forwireless communications by a base station (BS). The apparatus generallyincludes at least one processor configured to identify, within asubframe, a first search space for a user equipment (UE) to monitor fora downlink control channel that occupies a first number of physicalresource blocks (PRBs) that represents a narrowband size and transmitone or more downlink control channels to the UE in the first searchspace. Additionally, the apparatus generally includes a memory coupledwith the at least one processor.

Certain aspects of the present disclosure provide a computer programproduct for wireless communications by a base station (BS) comprising acomputer readable medium having instructions stored thereon. Theinstructions, when executed by at least one processor, causes theprocessor to identify, within a subframe, a first search space for auser equipment (UE) to monitor for a downlink control channel thatoccupies a first number of physical resource blocks (PRBs) thatrepresents a narrowband size and transmit one or more downlink controlchannels to the UE in the first search space.

Numerous other aspects are provided including methods, apparatus,systems, computer program products, and processing systems.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 is a block diagram conceptually illustrating an example of awireless communication network, in accordance with certain aspects ofthe present disclosure.

FIG. 2 shows a block diagram conceptually illustrating an example of abase station in communication with a user equipment (UE) in a wirelesscommunications network, in accordance with certain aspects of thepresent disclosure.

FIG. 3 is a block diagram conceptually illustrating an example of aframe structure in a wireless communications network, in accordance withcertain aspects of the present disclosure.

FIG. 4 is a block diagram conceptually illustrating two exemplarysubframe formats with the normal cyclic prefix, in accordance withcertain aspects of the present disclosure.

FIG. 5 illustrates an exemplary subframe configuration for eMTC, inaccordance with certain aspects of the present disclosure.

FIG. 6 illustrates a time/frequency grid of resource elements (REs), inaccordance with certain aspects of the present disclosure.

FIG. 7A illustrates an exemplary eCCE definition for a localized ePDCCH,in accordance with certain aspects of the present disclosure.

FIG. 7B illustrates an exemplary eCCE definition for a distributedePDCCH, in accordance with certain aspects of the present disclosure.

FIGS. 8 and 9 illustrate examples of symbols per eCCE for varioussubframe configurations, in accordance with certain aspects of thepresent disclosure.

FIG. 10 illustrates example operations for wireless communications, by auser equipment (UE), in accordance with certain aspects of the presentdisclosure.

FIG. 11 illustrates example operations for wireless communications, by abase station (BS), in accordance with certain aspects of the presentdisclosure.

FIGS. 12-15 illustrate example control channel search spaceconfigurations, in accordance with certain aspects of the presentdisclosure.

DETAILED DESCRIPTION

Aspects of the present disclosure provide techniques that may helpenable efficient communication between a base station and machine typecommunication (MTC) based user equipments (UEs). For example, thetechniques may provide a design for a control channel targeting MTC UEs,using a narrowband (e.g., a six-PRB) based search space forcommunication.

The techniques described herein may be used for various wirelesscommunication networks such as CDMA, TDMA, FDMA, OFDMA, SC-FDMA andother networks. The terms “network” and “system” are often usedinterchangeably. A CDMA network may implement a radio technology such asuniversal terrestrial radio access (UTRA), cdma2000, etc. UTRA includeswideband CDMA (WCDMA), time division synchronous CDMA (TD-SCDMA), andother variants of CDMA. cdma2000 covers IS-2000, IS-95 and IS-856standards. A TDMA network may implement a radio technology such asglobal system for mobile communications (GSM). An OFDMA network mayimplement a radio technology such as evolved UTRA (E-UTRA), ultra mobilebroadband (UMB), IEEE 802.11 (Wi-Fi), IEEE 802.16 (WiMAX), IEEE 802.20,Flash-OFDM®, etc. UTRA and E-UTRA are part of universal mobiletelecommunication system (UMTS). 3GPP Long Term Evolution (LTE) andLTE-Advanced (LTE-A), in both frequency division duplex (FDD) and timedivision duplex (TDD), are new releases of UMTS that use E-UTRA, whichemploys OFDMA on the downlink and SC-FDMA on the uplink. UTRA, E-UTRA,UMTS, LTE, LTE-A and GSM are described in documents from an organizationnamed “3rd Generation Partnership Project” (3GPP). cdma2000 and UMB aredescribed in documents from an organization named “3rd GenerationPartnership Project 2” (3GPP2). The techniques described herein may beused for the wireless networks and radio technologies mentioned above aswell as other wireless networks and radio technologies. For clarity,certain aspects of the techniques are described below forLTE/LTE-Advanced, and LTE/LTE-Advanced terminology is used in much ofthe description below. LTE and LTE-A are referred to generally as LTE.

A wireless communication network may include a number of base stationsthat can support communication for a number of wireless devices.Wireless devices may include user equipments (UEs). Some examples of UEsmay include cellular phones, smart phones, personal digital assistants(PDAs), wireless modems, handheld devices, tablets, laptop computers,netbooks, smartbooks, ultrabooks, wearables (e.g., smart glasses, smartrings, smart bracelets, smart clothing), etc. Some UEs may be consideredmachine-type communication (MTC) UEs, which may include remote devices,such as drones, robots, sensors, meters, location tags, etc., that maycommunicate with a base station, another remote device, or some otherentity. Machine type communication (MTC) may refer to communicationinvolving at least one remote device on at least one end of thecommunication and may include forms of data communication which involveone or more entities that do not necessarily need human interaction. MTCUEs may include UEs that are capable of MTC communications with MTCservers and/or other MTC devices through Public Land Mobile Networks(PLMN), for example.

FIG. 1 illustrates an example wireless communication network 100, inwhich aspects of the present disclosure may be practiced. For example,techniques presented herein may be used to help UEs and BSs shown inFIG. 1 communicate on a machine type communication physical downlinkcontrol channel (mPDCCH) using a narrowband (e.g., six-PRB) based searchspace.

The network 100 may be an LTE network or some other wireless network.Wireless network 100 may include a number of evolved Node Bs (eNBs) 110and other network entities. An eNB is an entity that communicates withuser equipments (UEs) and may also be referred to as a base station, aNode B, an access point, etc. Each eNB may provide communicationcoverage for a particular geographic area. In 3GPP, the term “cell” canrefer to a coverage area of an eNB and/or an eNB subsystem serving thiscoverage area, depending on the context in which the term is used.

An eNB may provide communication coverage for a macro cell, a pico cell,a femto cell, and/or other types of cell. A macro cell may cover arelatively large geographic area (e.g., several kilometers in radius)and may allow unrestricted access by UEs with service subscription. Apico cell may cover a relatively small geographic area and may allowunrestricted access by UEs with service subscription. A femto cell maycover a relatively small geographic area (e.g., a home) and may allowrestricted access by UEs having association with the femto cell (e.g.,UEs in a closed subscriber group (CSG)). An eNB for a macro cell may bereferred to as a macro eNB. An eNB for a pico cell may be referred to asa pico eNB. An eNB for a femto cell may be referred to as a femto eNB ora home eNB (HeNB). In the example shown in FIG. 1, an eNB 110 a may be amacro eNB for a macro cell 102 a, an eNB 110 b may be a pico eNB for apico cell 102 b, and an eNB 110 c may be a femto eNB for a femto cell102 c. An eNB may support one or multiple (e.g., three) cells. The terms“eNB”, “base station” and “cell” may be used interchangeably herein.

Wireless network 100 may also include relay stations. A relay station isan entity that can receive a transmission of data from an upstreamstation (e.g., an eNB or a UE) and send a transmission of the data to adownstream station (e.g., a UE or an eNB). A relay station may also be aUE that can relay transmissions for other UEs. In the example shown inFIG. 1, a relay station 110 d may communicate with macro eNB 110 a and aUE 120 d in order to facilitate communication between eNB 110 a and UE120 d. A relay station may also be referred to as a relay eNB, a relaybase station, a relay, etc.

Wireless network 100 may be a heterogeneous network that includes eNBsof different types, e.g., macro eNBs, pico eNBs, femto eNBs, relay eNBs,etc. These different types of eNBs may have different transmit powerlevels, different coverage areas, and different impact on interferencein wireless network 100. For example, macro eNBs may have a hightransmit power level (e.g., 5 to 40 Watts) whereas pico eNBs, femtoeNBs, and relay eNBs may have lower transmit power levels (e.g., 0.1 to2 Watts).

A network controller 130 may couple to a set of eNBs and may providecoordination and control for these eNBs. Network controller 130 maycommunicate with the eNBs via a backhaul. The eNBs may also communicatewith one another, e.g., directly or indirectly via a wireless orwireline backhaul.

UEs 120 (e.g., 120 a, 120 b, 120 c) may be dispersed throughout wirelessnetwork 100, and each UE may be stationary or mobile. A UE may also bereferred to as an access terminal, a terminal, a mobile station, asubscriber unit, a station, etc. A UE may be a cellular phone, apersonal digital assistant (PDA), a wireless modem, a wirelesscommunication device, a handheld device, a laptop computer, a cordlessphone, a wireless local loop (WLL) station, a tablet, a smart phone, anetbook, a smartbook, an ultrabook, etc. In FIG. 1, a solid line withdouble arrows indicates desired transmissions between a UE and a servingeNB, which is an eNB designated to serve the UE on the downlink and/oruplink. A dashed line with double arrows indicates potentiallyinterfering transmissions between a UE and an eNB.

FIG. 2 shows a block diagram of a design of base station/eNB 110 and UE120, which may be one of the base stations/eNBs and one of the UEs inFIG. 1. Base station 110 may be equipped with T antennas 234 a through234 t, and UE 120 may be equipped with R antennas 252 a through 252 r,where in general T≥1 and R≥1.

At base station 110, a transmit processor 220 may receive data from adata source 212 for one or more UEs, select one or more modulation andcoding schemes (MCS) for each UE based on CQIs received from the UE,process (e.g., encode and modulate) the data for each UE based on theMCS(s) selected for the UE, and provide data symbols for all UEs.Transmit processor 220 may also process system information (e.g., forSRPI, etc.) and control information (e.g., CQI requests, grants, upperlayer signaling, etc.) and provide overhead symbols and control symbols.Processor 220 may also generate reference symbols for reference signals(e.g., the CRS) and synchronization signals (e.g., the PSS and SSS). Atransmit (TX) multiple-input multiple-output (MIMO) processor 230 mayperform spatial processing (e.g., precoding) on the data symbols, thecontrol symbols, the overhead symbols, and/or the reference symbols, ifapplicable, and may provide T output symbol streams to T modulators(MODs) 232 a through 232 t. Each modulator 232 may process a respectiveoutput symbol stream (e.g., for OFDM, etc.) to obtain an output samplestream. Each modulator 232 may further process (e.g., convert to analog,amplify, filter, and upconvert) the output sample stream to obtain adownlink signal. T downlink signals from modulators 232 a through 232 tmay be transmitted via T antennas 234 a through 234 t, respectively.

At UE 120, antennas 252 a through 252 r may receive the downlink signalsfrom base station 110 and/or other base stations and may providereceived signals to demodulators (DEMODs) 254 a through 254 r,respectively. Each demodulator 254 may condition (e.g., filter, amplify,downconvert, and digitize) its received signal to obtain input samples.Each demodulator 254 may further process the input samples (e.g., forOFDM, etc.) to obtain received symbols. A MIMO detector 256 may obtainreceived symbols from all R demodulators 254 a through 254 r, performMIMO detection on the received symbols if applicable, and providedetected symbols. A receive processor 258 may process (e.g., demodulateand decode) the detected symbols, provide decoded data for UE 120 to adata sink 260, and provide decoded control information and systeminformation to a controller/processor 280. A channel processor maydetermine RSRP, RSSI, RSRQ, CQI, etc.

On the uplink, at UE 120, a transmit processor 264 may receive andprocess data from a data source 262 and control information (e.g., forreports comprising RSRP, RSSI, RSRQ, CQI, etc.) fromcontroller/processor 280. Processor 264 may also generate referencesymbols for one or more reference signals. The symbols from transmitprocessor 264 may be precoded by a TX MIMO processor 266 if applicable,further processed by modulators 254 a through 254 r (e.g., for SC-FDM,OFDM, etc.), and transmitted to base station 110. At base station 110,the uplink signals from UE 120 and other UEs may be received by antennas234, processed by demodulators 232, detected by a MIMO detector 236 ifapplicable, and further processed by a receive processor 238 to obtaindecoded data and control information sent by UE 120. Processor 238 mayprovide the decoded data to a data sink 239 and the decoded controlinformation to controller/processor 240. Base station 110 may includecommunication unit 244 and communicate to network controller 130 viacommunication unit 244. Network controller 130 may include communicationunit 294, controller/processor 290, and memory 292.

Controllers/processors 240 and 280 may direct the operation at basestation 110 and UE 120, respectively. For example, processor 240 and/orother processors and modules at base station 110 may perform directoperations 1100 shown in FIG. 11. Similarly, processor 280 and/or otherprocessors and modules at UE 120, may perform or direct operations 1000shown in FIG. 10. Memories 242 and 282 may store data and program codesfor base station 110 and UE 120, respectively. A scheduler 246 mayschedule UEs for data transmission on the downlink and/or uplink.

FIG. 3 shows an exemplary frame structure 300 for FDD in LTE. Thetransmission timeline for each of the downlink and uplink may bepartitioned into units of radio frames. Each radio frame may have apredetermined duration (e.g., 10 milliseconds (ms)) and may bepartitioned into 10 subframes with indices of 0 through 9. Each subframemay include two slots. Each radio frame may thus include 20 slots withindices of 0 through 19. Each slot may include L symbol periods, e.g.,seven symbol periods for a normal cyclic prefix (as shown in FIG. 3) orsix symbol periods for an extended cyclic prefix. The 2L symbol periodsin each subframe may be assigned indices of 0 through 2L−1.

In LTE, an eNB may transmit a primary synchronization signal (PSS) and asecondary synchronization signal (SSS) on the downlink in the center ofthe system bandwidth for each cell supported by the eNB. The PSS and SSSmay be transmitted in symbol periods 6 and 5, respectively, in subframes0 and 5 of each radio frame with the normal cyclic prefix, as shown inFIG. 3. The PSS and SSS may be used by UEs for cell search andacquisition. The eNB may transmit a cell-specific reference signal (CRS)across the system bandwidth for each cell supported by the eNB. The CRSmay be transmitted in certain symbol periods of each subframe and may beused by the UEs to perform channel estimation, channel qualitymeasurement, and/or other functions. The eNB may also transmit aphysical broadcast channel (PBCH) in symbol periods 0 to 3 in slot 1 ofcertain radio frames. The PBCH may carry some system information. TheeNB may transmit other system information such as system informationblocks (SIBs) on a physical downlink shared channel (PDSCH) in certainsubframes. The eNB may transmit control information/data on a physicaldownlink control channel (PDCCH) in the first B symbol periods of asubframe, where B may be configurable for each subframe. The eNB maytransmit traffic data and/or other data on the PDSCH in the remainingsymbol periods of each subframe.

FIG. 4 shows two exemplary subframe formats 410 and 420 with the normalcyclic prefix. The available time frequency resources may be partitionedinto resource blocks. Each resource block may cover 12 subcarriers inone slot and may include a number of resource elements. Each resourceelement may cover one subcarrier in one symbol period and may be used tosend one modulation symbol, which may be a real or complex value.

Subframe format 410 may be used for two antennas. A CRS may betransmitted from antennas 0 and 1 in symbol periods 0, 4, 7 and 11. Areference signal is a signal that is known a priori by a transmitter anda receiver and may also be referred to as pilot. A CRS is a referencesignal that is specific for a cell, e.g., generated based on a cellidentity (ID). In FIG. 4, for a given resource element with label Ra, amodulation symbol may be transmitted on that resource element fromantenna a, and no modulation symbols may be transmitted on that resourceelement from other antennas. Subframe format 420 may be used with fourantennas. A CRS may be transmitted from antennas 0 and 1 in symbolperiods 0, 4, 7 and 11 and from antennas 2 and 3 in symbol periods 1 and8. For both subframe formats 410 and 420, a CRS may be transmitted onevenly spaced subcarriers, which may be determined based on cell ID.CRSs may be transmitted on the same or different subcarriers, dependingon their cell IDs. For both subframe formats 410 and 420, resourceelements not used for the CRS may be used to transmit data (e.g.,traffic data, control data, and/or other data).

The PSS, SSS, CRS and PBCH in LTE are described in 3GPP TS 36.211,entitled “Evolved Universal Terrestrial Radio Access (E-UTRA); PhysicalChannels and Modulation,” which is publicly available.

An interlace structure may be used for each of the downlink and uplinkfor FDD in LTE. For example, Q interlaces with indices of 0 through Q−1may be defined, where Q may be equal to 4, 6, 8, 10, or some othervalue. Each interlace may include subframes that are spaced apart by Qframes. In particular, interlace q may include subframes q, q+Q, q+2Q,etc., where q∈{0, . . . , Q−1}.

The wireless network may support hybrid automatic retransmission request(HARQ) for data transmission on the downlink and uplink. For HARQ, atransmitter (e.g., an eNB) may send one or more transmissions of apacket until the packet is decoded correctly by a receiver (e.g., a UE)or some other termination condition is encountered. For synchronousHARQ, all transmissions of the packet may be sent in subframes of asingle interlace. For asynchronous HARQ, each transmission of the packetmay be sent in any subframe.

A UE may be located within the coverage of multiple eNBs. One of theseeNBs may be selected to serve the UE. The serving eNB may be selectedbased on various criteria such as received signal strength, receivedsignal quality, pathloss, etc. Received signal quality may be quantifiedby a signal-to-noise-and-interference ratio (SINR), or a referencesignal received quality (RSRQ), or some other metric. The UE may operatein a dominant interference scenario in which the UE may observe highinterference from one or more interfering eNBs.

As noted above, aspects of the present disclosure provide techniques forsignalling control channels to machine type communication (MTC) devicesusing a relatively narrow band of overall system bandwidth.

The focus of traditional LTE design (e.g., for legacy “non MTC” devices)is on the improvement of spectral efficiency, ubiquitous coverage, andenhanced quality of service (QoS) support. Current LTE system downlink(DL) and uplink (UL) link budgets are designed for coverage of high enddevices, such as state-of-the-art smartphones and tablets, which maysupport a relatively large DL and UL link budget.

However, low cost, low rate devices need to be supported as well. Forexample, certain standards (e.g., LTE Release 12) have introduced a newtype of UE (referred to as a category 0 UE) generally targeting low costdesigns or machine type communications. For machine type communication(MTC) or low cost UEs, generally referred to as MTC UEs, variousrequirements may be relaxed as only a limited amount of information mayneed to be exchanged. For example, maximum bandwidth may be reduced(relative to legacy UEs), a single receive radio frequency (RF) chainmay be used, peak rate may be reduced (e.g., a maximum of 100 bits for atransport block size), transmit power may be reduced, Rank 1transmission may be used, and half duplex operation may be performed.

In some cases, if half-duplex operation is performed, MTC UEs may have arelaxed switching time to transition from transmitting to receiving (orreceiving to transmitting). For example, the switching time may berelaxed from 20 μs for regular UEs to 1 ms for MTC UEs. Release 12 MTCUEs may still monitor downlink (DL) control channels in the same way asregular UEs, for example, monitoring for wideband control channels inthe first few symbols (e.g., PDCCH) as well as narrowband controlchannels occupying a relatively narrowband, but spanning a length of asubframe (e.g., ePDCCH).

Certain standards (e.g., LTE Release 13) may introduce support forvarious additional MTC enhancements, referred to herein as enhanced MTC(or eMTC). For example, eMTC may provide MTC UEs with coverageenhancements up to 15 dB.

As illustrated in the subframe structure 500 of FIG. 5, eMTC UEs cansupport narrowband bandwidth operation while operating in a wider systembandwidth (e.g., 1.4/3/5/10/15/20 MHz). In the example illustrated inFIG. 5, a conventional legacy control region 510 may span systembandwidth of a first few symbols, while a narrowband region 530 of thesystem bandwidth (spanning a narrow portion of a data region 520) may bereserved for an MTC physical downlink control channel (referred toherein as an mPDCCH) and for an MTC physical downlink shared channel(referred to herein as an mPDSCH). In some cases, an MTC UE monitoringthe narrowband region may operate at 1.4 MHz or 6 physical resourceblocks (PRBs). A PRB may comprise 12 consecutive subcarriers for oneslot in duration.

However, as noted above, eMTC UEs may be able to operate in a cell witha bandwidth larger than 6 RBs. Within this larger bandwidth, each eMTCUE may still operate (e.g., monitor/receive/transmit) while abiding by a6-PRB constraint. In some cases, different eMTC UEs may be served bydifferent narrowband regions (e.g., with each spanning 6-PRB blocks).

In Release 11, an enhanced physical downlink control channel (ePDCCH)was introduced. In contrast to the PDCCH which spans a first few symbolsin a subframe, the ePDCCH is frequency division multiplexing (FDM) basedand spans (symbols of) the entire subframe. Additionally, as compared tothe conventional PDCCH CRS support, the ePDCCH may only supportdemodulation reference signals (DM-RS).

In some cases the ePDCCH may be UE-specifically configured. For example,each UE in a network may be configured to monitor a different set ofresources for the ePDCCH. Additionally, the ePDCCH supports two modes ofoperation: localized ePDCCH, in which a single precoder is applied toeach PRB, and distributed ePDCCH, in which two precoders cycle throughthe allocated resources within each PRB pair.

The ePDCCH may be constructed based on enhanced resource element groups(eREGs) and enhanced control channel elements (eCCEs). Generally, aneREG is defined based on excluding DM-RS REs, assuming a maximum amountof DM-RS (e.g., 24 DM-RS REs for normal cyclic prefix and 16 DM-RS REsfor extended cyclic prefix) and including any non-DM-RS REs (e.g., REsthat do not carry DM-RS). Thus, for normal cyclic prefix, the number ofREs available for the ePDCCH is 144 (12 subcarriers×14 symbols−24DM-RS=144 REs), and, for extended cyclic prefix, the number of REsavailable for the ePDCCH is 128 (12 subcarriers*12 symbols−16 DM-RS=128REs).

In some cases, a PRB pair is divided into 16 eREGs, regardless ofsubframe type, cyclic prefix type, PRB pair index, subframe index, etc.Thus, for normal cyclic prefix, there are 9 REs per eREG and 8 REs pereREG for extended cyclic prefix. In some cases the eREG to RE mappingmay follow a cyclic/sequential and frequency-first-time-second manner,which may be beneficial for equalizing the number of available REs pereREG. Additionally, due to the presence of other signals, the number ofavailable REs for the ePDCCH may not be fixed and can be different fordifferent eREGs in a PRB pair.

FIG. 6 shows an example time/frequency grid of REs that illustrates 16eREGs sequentially defined in one PRB pair, excluding DM-RS REs. Asillustrated, the eREG to RE mapping may sequentially map REs of eacheREG, in a frequency-first, then time manner. That is, starting at RE(0, 0), the eREG index increases sequentially by increasing tone indexand then increasing symbol index. The number associated with each REdenotes the eREG index (0-15). For example, the 9 “15”s in FIG. 6 arethe 9 Res that make up eREG index 15. As noted above, the number of REsper eREG may be fixed at 9 for normal cyclic prefix. Additionally, aspictured, 24 DM-RS REs are not associated with any eREG.

In some cases, the number of eREGs per eCCE may be either four or eight.If normal cyclic prefix is used and a normal subframe or specialsubframe configurations 3, 4, or 8 (e.g., when the number of REs/PRBpair is large) are used, the number of eREGs per eCCE may be four (N=4),which corresponds to four eCCEs per PRB pair. Otherwise, the number ofeREGs per eCCE may be eight (N=8).

In some cases, eCCEs may be further based on an eREG grouping concept.For example, regardless of localized or distributed ePDCCH, 4 eREGgroups may be formed: Group #0: eREGs {0, 4, 8, 12}; Group #1: eREGs {1,5, 9, 13}; Group #2: eREGs {2, 6, 10, 14}; Group #3: eREGs {3, 7, 11,15}, where the numbers inside the braces indicate the eREG index aspictured in FIG. 6. In some cases, when an eCCE is formed by four eREGs,an eCCE may be formed by one eREG group. Additionally, when an eCCE isformed by eight eREGs, an eCCE may be formed by two eREG groups, whichmay be either group numbers 0 and 2 or 1 and 3.

In some scenarios, the location of eREGs of an eREG group may depend onthe ePDCCH mode. For example, for a localized ePDCCH, eREGs of the samegroup may always come from the same PRB pair. For a distributed ePDCCH,eREGs of the same group may come from different PRB pairs. The detailedmapping depends on the number of PRB pairs configured for ePDCCH.

As illustrated in FIG. 7A, for a localized ePDCCH, each eCCE may bedefined within one PRB pair (e.g., as illustrated, a single PRB pair j).For example, each different pattern illustrated in FIG. 7A may representone eCCE where the value in each box represents the eREG index. Forexample, as can be seen, eREG numbers 0, 4, 8, and 12 have the samepattern, which represents Group #0.

As illustrated in FIG. 7B, for a distributed ePDCCH, each eCCE may bedefined across different PRB pairs (e.g., PRB pairs 0-3). For example,as illustrated in FIG. 7B, eCCE #0 consists of eREG 0 of PRB pair 0,eREG 4 of PRB pair 1, eREG 8 of PRB pair 2, and eREG 12 of PRB pair 3.The four PRB pairs illustrated in FIG. 7B may not be contiguous infrequency (e.g., the PRB pairs may be frequency distributed).

As illustrated in FIG. 8, similar to eREG design, the number ofavailable REs per eCCE for ePDCCH may not be fixed and may be differentfor different eCCEs. However, as illustrated in FIG. 9, an eREG groupingbased eCCE definition may potentially help equalize the number ofavailable REs per eCCE, assuming two CRS ports, normal cyclic prefix,and normal subframes.

In some cases, each UE may be configured with up to two ePDCCH resourcesets (K=2), where each resource set is separately configured with M=2,4, or 8 PRB pairs. Additionally, each ePDCCH resource set may beseparately configured with either a localized or distributed mode.

In some cases, for a search space of a localized ePDCCH, the candidatesof a given aggregation layer (AL) may be spaced in as many different PRBpairs as possible so as to exploit sub-band scheduling for the ePDCCH asmuch as possible. On the other hand, the search space for a distributedePDCCH may be similar to a legacy PDCCH. In some cases (e.g., for LTERelease 11), REs occupied by other signals known to the UE (e.g., legacycontrol region, CRS, UE-specifically configured CSI-RS) may berate-matched around the ePDCCH.

As noted above, for normal UEs, an ePDCCH resource set may be configuredwith two, four, or eight PRB pairs. However, certain MTC UEs may beconfigured to operate in a narrowband, for example, using six PRB pairs,which may not match one of the defined ePDCCH resource setconfigurations. However, aspects of the present disclosure providesolutions for communicating on a control channel using such a narrowbandthat does not match a current ePDCCH resource set.

FIG. 10 illustrates example operations 1000 that may be performed by auser equipment (UE), such as an MTC or eMTC UE (e.g., one or more of theUEs 120). Operations 1000 begin, at 1002, by identifying, within asubframe, a first search space to monitor for a downlink control channelthat occupies a first number of physical resource blocks (PRBs) thatrepresents a narrowband size. According to certain aspects, the downlinkcontrol channel may comprise a machine type communication physicaldownlink control channel (mPDCCH). At 1004 the UE monitors at least thefirst search space for the downlink control channel transmitted in thesubframe. The UE receives the downlink control channel transmitted inthe subframe based, at least in part, on the monitoring (not pictured).In some aspects, the receiving comprises receiving information on thedownlink control channel using one subframe or a set of subframes (e.g.,the set of subframes comprises two or more subframes).

FIG. 11 illustrates example operations 1100 that may be performed by abase station (BS) (e.g., BS 110), for communicating with a userequipment (UE), such as an MTC or eMTC UE. The operations 1100 may beconsidered complementary to operations 1000 of FIG. 10.

Operations 1100 begin, at 1102, by identifying, within a subframe, afirst search space for a user equipment (UE) to monitor for a downlinkcontrol channel that occupies a first number of physical resource blocks(PRBs) that represents a narrowband size. At 1104, the BS transmits oneor more downlink control channels to the UE in the first search space.In some aspects, the transmitting comprises transmitting information onthe one or more downlink control channels using one subframe or a set ofsubframes (e.g., the set of subframes comprises two or more subframes).

Examples below assume a narrowband size of six-PRBs. Those skilled inthe art will recognize, however, that these are examples only and thatthe techniques presented herein may be more broadly applied to differentsizes of narrowband regions (e.g., narrowband sizes) of a wider systembandwidth. In aspects, a size of the narrowband region may depend on acategory of a UE or a capability of the UE. For example, MTC-type UEsmay communicate using a smaller region of bandwidth than non-MTC UEs.

As used herein, the term decoding candidate generally refers to adiscrete set of resources within a search space that might carry achannel to be decoded (e.g., a downlink control channel). Thus, a searchspace typically accommodates a number of different decoding candidates,with the number depending on various factors (such as the size ofdecoding candidates and whether decoding candidates are allowed tooverlap). As described in more detail below, aspects of the presentdisclosure provide different search space options, each withcorresponding decoding candidates, for transmitting a control channel.Thus, depending on the search space options, a base station will selectfrom available decoding candidates for transmitting a control channel,while a UE, in turn, will monitor the different possible decodingcandidates of each search space accordingly.

As illustrated in FIG. 12, one solution to allow for communication on acontrol channel utilizing a six-PRB based search space may be to have anMTC UE monitor all decoding candidates corresponding to a two PRB searchspace and/or a four PRB search space 1210, as well as one more candidate1220 that occupies all six PRBs. While this may mean that some UEs mayshare two-PRB and/or four PRB search spaces, but if the remaining PRBsare used for a UE mPDCCH, the entire six PRBs are used for the mPDCCH.

Thus, monitoring at 1004 may comprise monitoring a first search spacefor a downlink control channel decoding candidate spanning a firstnumber of PRBs (e.g., six PRBs) and also monitoring at least one of asecond search space or a third search space for a downlink controlchannel decoding candidate spanning the second and/or third searchspaces. In aspects, the first search space may comprise six PRBs and thesecond and/or third search spaces may comprise one, two, or four PRBs.Additionally, in aspects, the second and/or third search spaces maycomprise PRBs occupied by a another downlink control channel (e.g., anenhance physical downlink control channel (ePDCCH)).

Correspondingly, transmitting (1104) may comprise transmitting one ormore of the downlink control channels using resources in the firstsearch space corresponding to a downlink control channel decodingcandidate spanning the first number of PRBs or using resources in atleast one of the second search space or the third search spacecorresponding to a downlink control channel decoding candidate spanninga fewer number of PRBs than the first number of PRBs.

Additionally, according to certain aspects, the first search space(e.g., a search space occupying six PRBs, as noted above) may comprise acombination of the second and third search spaces (e.g., the two andfour-PRB search spaces). Thus, in some cases, monitoring 1004 maycomprise monitoring the first search space for a decoding candidate,transmitted by the base station (e.g., at 1104), with resources in boththe second and third search spaces. In some cases, the first searchspace may comprise a single decoding candidate.

According to certain aspects, the downlink control channel (e.g., themPDCCH) may be transmitted using a set of subframes (e.g., two or moresubframes). In this case, monitoring (1004) may comprise monitoring theset of subframes for the mPDCCH, wherein the set of subframes to monitoris determined/identified based, at least in part, on an indicationreceived from a serving network (e.g., the UE's serving base station).That is, the UE's serving base station may transmit and indication tothe UE of the set of subframes that the UE should monitor for themPDCCH.

Another solution to allow for communication on a control channel using asix-PRB based search space, as illustrated in FIG. 13, may be to definea six-PRB-based search space as a direct combination of the four-PRBsearch space 1310 and two-PRB based search space 1320. For example, withthe four-PRB block or the two-PRB block, an mREG/mCCE (e.g., the MTCresource element group and MTC control channel element, respectively)may be defined in the same manner as the eREG/eCCE of the ePDCCH.However, the mPDCCH search space may be defined based on mCCEs from thetwo blocks. For example, the mPDCCH search space may be defined based ona total of 24 mCCEs, as illustrated in FIG. 13.

According to certain aspects, one decoding candidate may have CCEs fromtwo blocks. For example, a candidate of aggregation level 16 may have 8CCEs from the first block and 8 CCEs from the second block. According tocertain aspects, the CCE indexing may be predefined, for example, byindexing the four-PRB based search space first followed by the two-PRBbased search space or the two-PRB based search space first followed bythe four-PRB based search space. According to certain aspects, differentUEs may have a different indexing scheme or the same indexing scheme.

Thus, monitoring (1004) may comprise monitoring for a decoding candidatehaving CCEs from two blocks (e.g., the two-PRB search space and thefour-PRB search space) according to a predefined CCE index. That is,monitoring (1004) may comprise searching within the a first search space(e.g., a combination of the two-PRB search space and the four-PRB searchspace) using a mapping of CCEs to resource element groups (REGs) basedon the size of the first search space. In some cases, the first searchspace in divided into a first set of control channel elements (CCEs) ofa first size corresponding to the second search space and a single CCEcorresponding to the third search space

According to certain aspects, defining a six-PRB based search space by adirect combination of the four-PRB and two-PRB based search spaces mayenable better sharing of the ePDCCH.

As illustrated in FIG. 14, another solution to allow for communicationon a control channel using a six-PRB based search space may be to have aUE configured with two mPDCCH resource sets (e.g., two-PRB search space1410 and four-PRB search space 1420). In this case, the UE may berequired to monitor decoding candidates separately defined within eachresource set and also one more decoding candidate 1430 spanning theentire six PRBs. For example, as illustrated in FIG. 14, the UE may bedesigned to monitor for decoding candidates in a first mPDCCH searchspace based on two-PRBs, a second mPDCCH search space based onfour-PRBs, and another search space using the entire six-PRBs. In otherwords, the 6-PRB candidate is possible when the total mPDCCH resourceset size is 6-PRB. Thus, according to certain aspects, transmitting(1104) may comprise transmitting the mPDCCH according to different setsof downlink control channel decoding candidates within each of the firstsearch space (e.g., the two-PRB search space), the second search space(e.g., the four-PRB search space), and the third search space (e.g., thesix-PRB search space). Additionally, monitoring (1004) may comprisemonitoring for downlink control channel decoding candidates within eachof the first, second, and third search spaces.

In some cases, for communicating on a control channel using a six-PRBbased search space, an mCCE to mREG mapping (e.g., based on six PRBs)may be defined.

As illustrated in FIG. 15, one solution for communication on a six-PRBbased search space may be to search a four-PRB search space 1510 andtreat a two-PRB block as a single large (“jumbo”) CCE 1520 as part ofthe search space. This large CCE 1520 may be combined with regularlydefined mCCEs (e.g., of four-PRB search space 1510). For example, a UEmay monitor a decoding candidate using mCCE 15 and the large mCCE 16 ormCCE 0-15 and the large mCCE 16 for all six-PRBs.

As noted above, aspects of the present disclosure provide varioustechniques for signalling control channels to machine type communication(MTC) devices using a relatively narrowband of overall system bandwidth.

As used herein, a phrase referring to “at least one of” a list of itemsrefers to any combination of those items, including single members. Asan example, “at least one of: a, b, or c” is intended to cover: a, b, c,a-b, a-c, b-c, and a-b-c.

The various operations of methods described above may be performed byany suitable means capable of performing the corresponding functions.The means may include various hardware and/or software/firmwarecomponent(s) and/or module(s), including, but not limited to a circuit,an application specific integrated circuit (ASIC), or processor.Generally, where there are operations illustrated in Figures, thoseoperations may be performed by any suitable corresponding counterpartmeans-plus-function components.

For example, means for identifying and/or means for monitoring mayinclude one or more processors, such as the receive processor 258 and/orthe controller/processor 280 of the user terminal 120 illustrated inFIG. 2 and/or the transmit processor 220 and/or the controller/processor240 of the base station 110 illustrated in FIG. 2. Means for receivingmay comprise a receive processor (e.g., the receive processor 258)and/or an antenna(s) 252 of the user terminal 120 illustrated in FIG. 2.Means for transmitting may comprise a transmit processor (e.g., thetransmit processor 220) and/or an antenna(s) 234 of the eNB 110illustrated in FIG. 2.

Those of skill in the art would understand that information and signalsmay be represented using any of a variety of different technologies andtechniques. For example, data, instructions, commands, information,signals, bits, symbols, and chips that may be referenced throughout theabove description may be represented by voltages, currents,electromagnetic waves, magnetic fields or particles, optical fields orparticles, or combinations thereof.

Those of skill would further appreciate that the various illustrativelogical blocks, modules, circuits, and algorithm steps described inconnection with the disclosure herein may be implemented as electronichardware, software/firmware, or combinations thereof. To clearlyillustrate this interchangeability of hardware and software/firmware,various illustrative components, blocks, modules, circuits, and stepshave been described above generally in terms of their functionality.Whether such functionality is implemented as hardware orsoftware/firmware depends upon the particular application and designconstraints imposed on the overall system. Skilled artisans mayimplement the described functionality in varying ways for eachparticular application, but such implementation decisions should not beinterpreted as causing a departure from the scope of the presentdisclosure.

The various illustrative logical blocks, modules, and circuits describedin connection with the disclosure herein may be implemented or performedwith a general-purpose processor, a digital signal processor (DSP), anapplication specific integrated circuit (ASIC), a field programmablegate array (FPGA) or other programmable logic device, discrete gate ortransistor logic, discrete hardware components, or any combinationthereof designed to perform the functions described herein. Ageneral-purpose processor may be a microprocessor, but in thealternative, the processor may be any conventional processor,controller, microcontroller, or state machine. A processor may also beimplemented as a combination of computing devices, e.g., a combinationof a DSP and a microprocessor, a plurality of microprocessors, one ormore microprocessors in conjunction with a DSP core, or any other suchconfiguration.

The steps of a method or algorithm described in connection with thedisclosure herein may be embodied directly in hardware, in asoftware/firmware module executed by a processor, or in a combinationthereof. A software/firmware module may reside in RAM memory, flashmemory, ROM memory, EPROM memory, EEPROM memory, phase change memory,registers, hard disk, a removable disk, a CD-ROM, or any other form ofstorage medium known in the art. An exemplary storage medium is coupledto the processor such that the processor can read information from, andwrite information to, the storage medium. In the alternative, thestorage medium may be integral to the processor. The processor and thestorage medium may reside in an ASIC. The ASIC may reside in a userterminal. In the alternative, the processor and the storage medium mayreside as discrete components in a user terminal.

In one or more exemplary designs, the functions described may beimplemented in hardware, software/firmware, or combinations thereof. Ifimplemented in software/firmware, the functions may be stored on ortransmitted over as one or more instructions or code on acomputer-readable medium. Computer-readable media includes both computerstorage media and communication media including any medium thatfacilitates transfer of a computer program from one place to another. Astorage media may be any available media that can be accessed by ageneral purpose or special purpose computer. By way of example, and notlimitation, such computer-readable media can comprise RAM, ROM, EPROM,EEPROM, flash memory, phase change memory, CD/DVD or other optical diskstorage, magnetic disk storage or other magnetic storage devices, or anyother medium that can be used to carry or store desired program codemeans in the form of instructions or data structures and that can beaccessed by a general-purpose or special-purpose computer, or ageneral-purpose or special-purpose processor. Also, any connection isproperly termed a computer-readable medium. For example, if thesoftware/firmware is transmitted from a website, server, or other remotesource using a coaxial cable, fiber optic cable, twisted pair, digitalsubscriber line (DSL), or wireless technologies such as infrared, radio,and microwave, then the coaxial cable, fiber optic cable, twisted pair,DSL, or wireless technologies such as infrared, radio, and microwave areincluded in the definition of medium. Disk and disc, as used herein,includes compact disc (CD), laser disc, optical disc, digital versatiledisc (DVD), floppy disk and Blu-ray disc where disks usually reproducedata magnetically, while discs reproduce data optically with lasers.Combinations of the above should also be included within the scope ofcomputer-readable media.

The previous description of the disclosure is provided to enable anyperson skilled in the art to make or use the disclosure. Variousmodifications to the disclosure will be readily apparent to thoseskilled in the art, and the generic principles defined herein may beapplied to other variations without departing from the spirit or scopeof the disclosure. Thus, the disclosure is not intended to be limited tothe examples and designs described herein but is to be accorded thewidest scope consistent with the principles and novel features disclosedherein.

What is claimed is:
 1. A method for wireless communications by a userequipment (UE), comprising: identifying, within a subframe, a firstsearch space to monitor for a downlink control channel that occupies afirst number of physical resource blocks (PRBs) that represents anarrowband size; and monitoring at least the first search space for thedownlink control channel transmitted in the subframe.